The history of Delhi is often talked about in terms of its seven cities. These were fortified settlements, established by various rulers between the eleventh and seventeenth centuries, now swallowed by the extensive city of today. The sixth Delhi is the Purana Qila, or Old Fortress, a 16th century stone fortress near the eastern edge of the city, and a particularly good place to tell the story of Delhi's urban development.

There are monuments in Delhi older than Qila, and certainly there are others more impressive. But it is unlikely that there is another place in the city where history is so deep. Excavations in the fort show that the area was inhabited in five previous Delhis, and even earlier, according to reports, until 300 BC. Some also believe that somewhere under the Qila are the remains of a legendary city that is a kind of civilizational navel. The aura of this city - Delhi zero? - It has attracted kings and governments and has allowed it to maintain its curious influence on the evolution of the city.

The walls of Qila and the few structures inside (a step, a squat tower used as a library-observatory and a fine mosque) are attributed to the Mughal emperor Humayun and the Afghan Sher Shah Suri ('The Lion King', rivals who ruled Delhi in the mid-16th century Humayun's construction began in 1533, but it was deposed after a few years by Sher Shah Humayun recaptured the fort 15 years later, but shortly thereafter he went down the library stairs and died. The Mughal chronicler of the time mentions that the Humayun Fort was built on the sacred site of Indraprastha, a story that sits in the gleaming realm between myth and history.